In the application of robotics, it is sometimes necessary to distinguish a painted portion of a surface from a surrounding surface that may be quite smooth, giving rise to specular reflection of incident light. In particular, in applying the methods of U.S. Pat. Nos. 4,337,566 and 4,355,447 in which holes or grooves are cut into a surface, painted, and the diameter visually monitored in a feedback loop controlling the machining of the surface, the specular reflection of the newly machined surface can make the painted surface indistinguishable.
The present invention provides an arrangement to enhance the visual detection of the painted areas relative to the surrounding material.